1. Field of the Invention
This invention relates to a thermostatic expansion valve in a refrigerant system for air conditioners of cars, and in particular, to an improvement in the internal structure of such thermostatic expansion valves of a type having a built-in thermosensitive mechanism.
2. Description of the Prior Art
FIG. 3 is an explanatory view showing an arrangement of refrigerating cycle of an air conditioner. The refrigerating cycle generally labelled 1 includes a compressor 4 driven by a motor 2, or the like, a condenser 5, a reservoir 6 containing a refrigerant condensed and liquidized by the condenser, a expansion valve 10 controlling the amount of the liquid refrigerant to pass through, and an evaporator 8.
The expansion valve 10 has a thermal sensor 10a which detects the temperature of the refrigerant near the exit of the evaporator 8, and a pipe 10b for equalizing a diaphragm the expansion valve has, such that these values are fed back to the expansion valve 10 to adjust the rate of the opening.
Numeral 11 denotes a pipe system of the refrigerating system, and 12 denotes a fan for introducing external air into the condenser 5.
Air conditioners for use in cars, for example, generally include a thermostatic expansion valve having a built-in thermosensitive mechanism in order to save its mounting space or to omit wiring.
FIG. 4 is a view showing a general arrangement of an existing expansion valve.
A valve housing 30 of the thermostatic expansion valve defines first and second passages 32 and 34, vertically isolated from each other. The first passage 32 is interposed in a part of the refrigerant pipe system 11, extending from the refrigerant outlet of the condenser 5 via the reservoir 6 toward the refrigerant inlet of the evaporator 8. The second passage is interposed in a part of the refrigerant pipe system 11, extending from the refrigerant outlet of the evaporator 8 toward the refrigerant inlet of the compressor 4.
The first passage 32 includes a valve hole 32a for adiabatically expanding the liquid-phase refrigerant supplied from the refrigerant outlet of the reservoir 6. The center line of the valve hole 32a extends in the length direction of the valve housing 30. The valve hole 32a defines a valve seat at its inlet, which can be seated by a valve member 32b energized by a biasing means 32c such as compression coil spring.
The first passage 32, to which the liquid-phase refrigerant is supplied from the reservoir 6, behaves as the passage of the liquid-phase refrigerant, and includes an inlet port 321 and a valve chamber 35 continuous from the inlet port 321. The valve chamber 35 is a chamber concentrically aligned with the valve hole 32a and sealed at the bottom by a plug 37.
Mounted at the top end of the valve housing 30 is a valve driving unit 36 for driving the valve member 32b. The valve driving unit 36 has a pressure-operating housing 36d which defines an interior hollow partitioned by a diaphragm 36a into two upper and lower pressure-operating chambers, 36b and 36c.
The lower pressure-operating chamber 35c in the pressure-operating housing 36d communicates with the second passage 34 via an equalizing opening 36e which is concentric with the valve hole 32a.
Introduced into the second passage 34 is the vapor-phase refrigerator from the refrigerant outlet of the evaporator 8. Thus the second passage 34 behaves as a passage for vapor-phase refrigerant to apply the pressure of the vapor-phase refrigerant to the lower pressure-operating chamber 36c via the equalizing opening 36e.
Concentrically disposed in and beyond the equalizing opening 36e is a valve driving rod 36f extending from the lower surface of the diaphragm 36a to the valve hole 32a of the first passage 32. The valve driving rod 36f is supported for vertical slidable movements by an inner surface of the lower pressure-operating chamber 36c of the pressure-operating housing 36d and by a partition wall of the valve housing 30 separating the first passage 32 from the second passage 34, and its lower end is fixed to the valve member 32b. The valve driving rod 36f has a sealing member 36g on its outer circumferential surface of its part located in the partition wall in order to prevent the refrigerant from entering from the first passage 32 to the second passage 34, and vice versa.
The upper pressure-operating chamber 36b of the pressure-operating housing 36d is filled with a known fluid for driving the diaphragm. The vapor-phase refrigerant introduced into the second passage 34 from the evaporator 8 transmits its heat to the diaphragm-driving fluid via the valve driving rod 36f exposed to the vapor-phase refrigerator in the second passage 34 and the equalizing opening 36e.
The diaphragm-driving fluid in the upper pressure-operating chamber 36b is changed to a gaseous phase in response to the transmitted heat, and applies a pressure onto the upper surface of the diaphragm 36a. The diaphragm 36a is displaced vertically by a difference between the pressure of the diaphragm driving gas applied to the upper surface of the diaphragm 36a and the pressure applied to the lower surface of the diaphragm 36a.
The vertical displacement of the central portion of the diaphragm 36a causes the valve driving rod 36f to move vertically to bring the valve member 32b to or away from the valve seat at the valve hole 32a. As a result, the flow amount of the refrigerant is controlled.
In expansion valves of this type, it is desirable that the refrigerant delivered from the reservoir 6 is all in the vapor phase. In some cases, however, the gaseous-phase refrigerant is mixed in the reservoir and sent to the inlet port 321 in a mixed vapor-and-liquid phase. The refrigerant including a part in the gaseous phase is liable to generate a noise when running through the inlet port 321, valve chamber and valve seat into the outlet passage.